1. Field of the Invention
The present invention relates to a photocurable coating composition, and to an overprint and a process for producing same. More particularly, the present invention relates to a photocurable coating composition that is curable upon exposure to actinic radiation such as an electron beam or UV rays. In particular, it relates to a photocurable coating composition for coating an image formed by depositing ink and/or toner on a printing substrate (image receiving substrate) by a method such as lithography, relief printing, intaglio printing, screen printing, inkjet, or electrophotography. More particularly, it relates to a photocurable overprint composition (overprint composition) particularly suitably used for coating a toner-based printed material printed by an electrophotographic process.
2. Description of the Related Art
In recent years, a large number of actinic radiation curable compositions that can be used in UV curable printing inks, paints, and coatings have been developed, and the spreading thereof is currently being promoted. However, it is at present difficult to obtain a photocurable composition that satisfies all requirements in terms of curability, surface smoothness, strength, storage stability, etc.
In particular, when a layer of fuser oil is present on the surface of a toner-based image such as one obtained by an electrophotographic process, it is yet more difficult to obtain desired performance.
In a standard method for forming a toner-based image, such as an electrophotographic process, an electrostatic charge is formed on a latent image retaining surface by uniformly charging a latent image retaining surface such as, for example, a photoreceptor. Subsequently, charge on the uniformly charged region is selectively released by a pattern of activation irradiation corresponding to an original image. The latent image charge pattern remaining on the surface corresponds to regions that have not been exposed to radiation. Subsequently, the photoreceptor is passed through one or a plurality of development housings containing toner, and since the toner is deposited on the charge pattern by electrostatic attractive force, the latent image charge pattern is visualized. Subsequently, the developed image is either fixed on an image-forming surface or transferred to a printing substrate such as, for example, paper and fixed thereto by an appropriate fixation technique, thus giving an electrophotographically printed material, that is, a toner-based printed material.
As a known method for protecting a printed material, applying an overprint coating to the printed material has been proposed. For example, JP-A-11-70647 and JP-A-2003-241414 (JP-A denotes a Japanese unexamined patent application publication) propose a method such as an electrophotographic process, in which fixation is carried out after a transparent toner is transferred on top of a toner-based image, thus covering the surface.
Furthermore, JP-A-61-210365 proposes a method in which an overprint coating is applied by applying a liquid film coating that is curable by UV rays, etc. and polymerizing (crosslinking) a coating component by means of light.
Furthermore, JP-A-2005-321782 discloses an overprint composition comprising a radiation curable oligomer selected from the group consisting of trifunctional unsaturated acrylic resins, a radiation curable monomer selected from the group consisting of polyfunctional alkoxylated acrylic monomers and polyalkoxylated acrylic monomers, such as one type or a plurality of types of diacrylate or triacrylate, at least one type of photopolymerization initiator, and at least one type of surfactant.